My Win 7 32-bit computer was running fine for several days after adding 2 new 1GB memory sticks to 2 512 sticks. Shut down at night and wouldn't power up in the morning. Nothing, no disks spinning, fans running, etc. All that happens when I push the power on button is that power LED flashes momentarily. Pushing button again elicits nothing. Turning rear switch off and then on again and then hitting power on results in the initial quick LED flash. Thought this must be a power unit failure although the motherboard LED comes on when rear power switch is on. I have double-checked the case's power switch connections as well as the motherboard's.

So I bought a new 500 watt power supply unit -- Same result
So I bought and replaced CMOS battery & re-set --Same result
So I bought a new (used) motherboard -- Same result
So I bought a new Intel 3.4 chip -- Same result
So I bought a new case for a new power switch --Same result

So now I am without a clue. Could memory all be bad; have run OK for awhile and just quit with no indication?

Unfortunately, I have no way to test the memory since I can't get the desktop to start and the laptop I'm using here won't accommodate. Out considerable money now; hate to buy all new memory. Tried a different power cord and a direct connection to a wall socket--same result. I'd take the memory to a repair shop for a check but they'll charge almost as much as new memory. I'm old and have no friends with computers they'd let me experiment with. Looks as though the best bet would be to start over and build a new desktop when I get flush again. Anybody have any suggestions about a brand new ATX motherboard? Not a gamer or player; might like to do some video editing some time in future

If a mod sees this please move it to the hardware forum.
About your problem, if you just installed new ram into your computer, shut it down and it refuses to come on...
Please remove your new ram for me and try to clear cmos for me and see what happens.

Also check your wiring again and make sure 24 pin atx connector is plugged in the 4 pin atx connector and the system led wires are properly hooked up.

Thanks for your reply. Sorry I screwed up putting this in the wrong forum initially. As to wiring, my only question would be with the new 500 w. power supply unit which, unlike the replaced one, has 24 pin + 4 on the same wire group as well as a wire group with two 4-pins. The directions seemed to indicate that I should use the double 4pin for the four pin connector and ignore the 4-pin with the 24 pin connector, just connecting the 24 pin. But note that the failure occurred with the connections of the old power supply in the same way it has ever since. I have double-checked the front power switch connections and power LED and reset--using the white wires as ground and the color wires as positive. I'll try removing the new memory and clearing the cmos as you suggest.

When I take the two new 1GB sticks out, computer won't start, but the instructions are to populate the blue 1 & 3 slots, so when I do this with the remaining two 512 sticks, the computer starts. Huhray! Thank you. When I take out the two 512 sticks and put the two 1 GB sticks in 1 & 3 slots, the computer starts! Still better. When I put back in the two 512 sticks in 2 & 4 slots, it won't start. When I get the other two 512 sticks I had originally and plug them in the with the two 1 GB, computer starts.
I don't understand this. But before it boots my system is suggests a memory diagnostic; I choose it and it almost immediately tells me there is a hardware problem and the machine will have to go back to the manufacturer, but the memory test keeps running. Apparently will for another hour or two at least.

This would seem to mean the 1GB sticks and the 512mb Crucial sticks are incompatible. But they are both the same type of 184 pin unbuffered DIMMs so far as I could tell from the sales specs. So I am going to have to buy two more 1 GB sticks after all to get 3.4GB total. Bummer, but thanks to Mike, b1 gapl and all. Sorry about the cross posting. Won't happen again.

Thanks for your reply. Sorry I screwed up putting this in the wrong forum initially. As to wiring, my only question would be with the new 500 w. power supply unit which, unlike the replaced one, has 24 pin + 4 on the same wire group as well as a wire group with two 4-pins. The directions seemed to indicate that I should use the double 4pin for the four pin connector and ignore the 4-pin with the 24 pin connector, just connecting the 24 pin. But note that the failure occurred with the connections of the old power supply in the same way it has ever since. I have double-checked the front power switch connections and power LED and reset--using the white wires as ground and the color wires as positive. I'll try removing the new memory and clearing the cmos as you suggest.

When I take the two new 1GB sticks out, computer won't start, but the instructions are to populate the blue 1 & 3 slots, so when I do this with the remaining two 512 sticks, the computer starts. Huhray! Thank you. When I take out the two 512 sticks and put the two 1 GB sticks in 1 & 3 slots, the computer starts! Still better. When I put back in the two 512 sticks in 2 & 4 slots, it won't start. When I get the other two 512 sticks I had originally and plug them in the with the two 1 GB, computer starts.
I don't understand this. But before it boots my system is suggests a memory diagnostic; I choose it and it almost immediately tells me there is a hardware problem and the machine will have to go back to the manufacturer, but the memory test keeps running. Apparently will for another hour or two at least.

This would seem to mean the 1GB sticks and the 512mb Crucial sticks are incompatible. But they are both the same type of 184 pin unbuffered DIMMs so far as I could tell from the sales specs. So I am going to have to buy two more 1 GB sticks after all to get 3.4GB total. Bummer, but thanks to Mike, b1 gapl and all. Sorry about the cross posting. Won't happen again.

Yeah thats rhe reason why I wanted you to take out your new ram and try the original to see what would happen.
The Problem I see here is incompatible ram with new or there is a memory limit on your mobo.
If your trying to go for 2gb's I would recommend you take the highest ram which might be DDR400 and put that in slot 1,
Take your second memory stick and put that into the 4 slot, turn it on and see if it will post.
If it does, try to limit the memory speed by DDR300 so that the other 2 memory sticks will follow suit and try to initialize.
Sometimes it works other times it won't, you just have to accomadate for what you have for now.

@MoM I don't know whats going with his postings, but I saw the one in windows and helped him out and asked it be moved. :\

OK, so it started up but it wouldn't boot up with the two 1 GB and the two 512 mb, even with the original CD. So I took out the 512s; still wouldn't boot up--Windows helpfully says "A required hardware unit is missing"--and roots me to the CD for repair. After running through all its tests, it reports: "Root Cause Found: ACLs on file J:\windows\system32\E9f410C18A.sys are not proper: Old value = 0x1219f." and then indicates it fixed it in some unspecified way. So anyway I'm working again. Thank you.

Mike, the memory limit on the ASUS P4P800 is 4 GB but in practice you only get 3.4 or something if you fill all 4 slots with 1GB. I had had 4 512mb sticks before, so the idea was to get at least 3gb RAM with two new 1 GB sticks. The ASUS manual is pretty insistent on using 1 and 3 slots for identical sized, etc. sticks, and letting you fill in with others on 2 and 4. But you may know better. It's just I wouldn't know how to limit the speed of the faster sticks to match the slower. I'm so happy to have 2GB RAM working again, I won't lust after three again until I can afford it. Thanks to you, to b1 gapl for the tips on memtest, and MOM and Slay for getting my posts straightened out into one thread. Next time I will check here first--but "proper", like Win7 advises.